A pin block or wrestplank is a laminated plank that sits under the iron plate at the front of the piano, where it defines a plurality of holes for receiving steel tuning pins. An end of each piano string is wrapped about the end of a corresponding tuning pin. The tuning pins are rotated in the pin block holes to tighten each piano string up to concert pitch. The pin blocks must hold the tuning pin tightly enough against loosening to allow the piano to stay in tune.
Multi-laminate wood planks used for less expensive pin blocks often have layers of glue of excessive thickness or excessive quantity of layers, which may lead to tuning instability. Many pin blocks or wrestplanks include layers of wood. Constant turning of the tuning pin can rapidly wear down the wood and enlarge the tuning pin hole, which eventually reduces the ability of the pin block to hold the tuning pin against loosening.
Different manufacturers vary the number of laminations (i.e. layers) forming the pin block. For example, a Steinway piano typically contains a pin block with six or seven thick laminations, e.g. often about ⅛ inch to about 5/16 inch in thickness, of maple, beech, and/or bubinga hardwoods, with the direction of grain in each layer disposed at an angle of approximately 45° to the direction of grain in opposing surfaces of adjacent layers. Other piano manufacturers provide pin blocks with seven or more laminations, in which the direction of grain in each layer is disposed substantially perpendicular to the direction of grain in opposing surfaces of adjacent layers.